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Sand dunes are unique ecosystems with distinct features which limited the accumulation of biomass. The distance from seashore affects both the physical properties of the sand dunes and the biota living above- and below ground. The goal of the present study was to determine the effects of the distance from shore to inland on soil bacterial community composition during wet and dry season. We studied a chronosequence of sites close to the eastern Mediterranean coast. Bacterial diversity was assessed using directly extracted DNA from soil samples and 16 S ribosomal RNA gene fingerprinting. Our data indicates a significant influence of season and site on bacterial community structure. We showed that during the wet season soil organic matter, pH and salinity strongly influence bacterial community composition, whereas during the dry period bacterial diversity was mainly driven by the shortage of water at all sites. Consequently diversity was lowest during dry season at dunes close to the shore, whereas during the wet season the higher water content and the reduced salinity at the dunes which are more at the inland induced an increase in diversity, which illustrates the pronounced dynamics of microbial communities in soil over a season mainly at inland dunes.

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Background: The wild radishes, Raphanus raphanistrum and R. pugioniformis (Brassicaceae) are native to the East Mediterranean region. However, whereas R. raphanistrum is widely distributed worldwide, the endemic R. pugioniformis is limited to specific habitats. In R. raphanistrum the diaspores of the indehiscent fruits comprise glabrous, light, single-seeded segments, whereas the intact fruits of R. pugioniformis are heavy and covered with spiny backwardpointing trichomes. We aimed to investigate whether the structure of the diaspores was directly associated with longand short-range dispersal in R. raphanistrum and R. pugioniformis, respectively. We further surveyed within-population spatial distributions, to test the hypothesis that short-and long-range dispersal contribute to a patchy vs. uniform distribution patterns of R. pugioniformis and R. raphanistrum, respectively. Results: The results indicated that dispersal by wind and runoff water was substantially lower for diaspores of R. pugioniformis than for those of R. raphanistrum diaspores. Supporting the hypothesis that backward-pointing trichomes promote adherence to soil particles, the displacement on soil surface of R. pugioniformis fruits depended on their orientation relative to wind direction. Furthermore, trichome removal from fruits of R. pugioniformis significantly reduced wind velocity needed to remove fruits that were placed on soils typical of the species' natural habitats. The spatial-distribution survey results indicated a patchy distribution of R. pugioniformis populations as compared with the more uniform arrangement in the studied populations of R. raphanistrum; consistent with the unidirectional vs. homogeneous wind dispersal of the respective diaspores, with respect to wind direction. In addition, R. pugioniformis population sizes changed less between years than those of R. raphanistrum. Conclusions: Overall, our results indicate that fruit structure is strongly linked to dispersal ability and spatial distribution of the two closely related wild radish species. Whereas R. raphanistrum inhabits homogenous sandy soil habitats, the distribution range of R. pugioniformis includes heterogeneous environments in which growth niches are scarcer. We suggest that the different modes of dispersal have evolved as adaptive traits appropriate to the species' specific habitats.